Overlock sewing machine

ABSTRACT

An overlock sewing machine which can readily form a rolled seam with no requirement for a complicated tension adjusting operation is disclosed. In this overlock sewing machine, an auxiliary thread tensioner (15) is provided independently of a main thread tensioner (4), providing a lower looper thread (9) with thread tension which is necessary for forming an over-edge chain stitch, in the vicinity thereof. An end cam (25) is provided on a shaft (13) of a dial (12) for feed adjustment, so that an upper pawl (23) rams one portion of the peripheral edge of a tension disc (20) and expands a side which is opposed thereto for canceling tension provision to the lower looper thread (9) passed through tension discs and provides the tension only by the main thread tensioner (4) to carry out an ordinary over-edge chain stitch when a lower pawl (24) is engaged with a high lift part of the end cam (25). In a rolled seam, the lower pawl (24) is engaged with a lower lift part of the end cam (25) by a rotational operation of the dial (12), and the upper pawl (23) is detached from the tension disc (20). Thus, tension which is provided by the auxiliary thread tensioner (15) in addition to the main thread tensioner (4) is applied to the lower looper thread (9), and it is not necessary to carry out tension adjustment in switching between the over-edge chain stitch and the rolled seam.

FIELD OF THE INVENTION

The present invention relates to an overlock sewing machine, and moreparticularly, it relates to an overlock sewing machine which can readilyswitch from an ordinary over-edge chain stitch to a rolled seam.

BACKGROUND TECHNIQUE

In general, a rolled seam is formed by employing an overlock sewingmachine with one needle and three threads or an overlock sewing machinewith one needle and two threads comprising a hook looper, replacing apresser foot and a needle plate with those for the rolled seam, andincreasing the tension of a lower looper thread or a looper thread(hereinafter referred to as a bobbin thread) while reducing the feedrate. FIG. 1 shows an ordinary over-edge chain stitch which is formed bya conventional overlock sewing machine with one needle and threethreads, and FIG. 2 shows a conventional rolled seam which is formed byincreasing bobbin thread tension (to about twice that in an ordinaryover-edge chain stitch) and reducing the feed rate for retracting anupper looper thread to the back side of cloth while reducing the seampitch. Referring to FIGS. 1 and 2, the over-edge chain stitch part andthe rolled seam part are formed by needle threads 101, upper looperthreads 102 and lower looper threads 103.

Such a rolled seam is generally employed for an over-edge chain stitchfor a handkerchief or the like since the cloth edge is rolled andbeautified on the upper part.

In most of conventional general overlock sewing machines, it has beennecessary to replace parts such as a presser foot and a needle platewith those which are dedicated for a rolled seam while strengtheningtension of a bobbin thread in the case of forming the rolled seam, ashereinabove described. In this adjustment of the tension, there has beensuch a problem that an adjustment operation for attaining preferabletension balance is not easy due to a seam by complicated intertwinementof a plurality of threads, and a considerable time is required as theresult. This also applies to the case of returning the operation fromthe rolled seam to an ordinary over-edge chain stitch, and there hasbeen such a problem that the presser foot and the needle plate arechanged to ordinary standard parts while a complicated adjustmentoperation for attaining preferable tension balance which is suitable forthe over-edge chain stitch is required.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an overlock sewingmachine which can readily perform switching from an over-edge chainstitch to a rolled seam or reverse switching without carrying out acomplicated tension adjustment operation.

The overlock sewing machine according to the present invention comprisesa main thread tensioner for providing a bobbin thread with threadtension which is necessary for forming an ordinary over-edge chainstitch, and an auxiliary thread tensioner for providing the bobbinthread with thread tension which is necessary for forming a rolled seamalong with the main thread tensioner. Thus, it is not necessary to carryout adjustment of the thread tension for forming a rolled seam orreturning the rolled seam to an ordinary over-edge chain stitch andtension balance which is once attained may not be changed, wherebyswitching from the over-edge chain stitch to the rolled seam or reverseswitching is simplified. Further, tension adjustment ranges can benarrowed in both of the main thread tensioner and the auxiliary threadtensioner as compared with that carrying out tension adjustment in awide range from the over-edge chain stitch to the rolled seam with onethread tensioner by one thread tensioner, whereby the degree of freedomin design of the thread tensioners is advantageously increased.

In the overlock sewing machine according to the present invention, thebobbin thread is guided along the main thread tensioner and theauxiliary thread tensioner for the rolled seam to be provided withthread tension from the two thread tensioners, while the bobbin threadis guided along only the main thread tensioner for the over-edge chainstitch along a thread path which is different from that for the rolledseam not to be passed through the auxiliary thread tensioner, or passedthrough the auxiliary thread tensioner along the same path as that forthe rolled seam and tension provision of the auxiliary tensioner iscanceled. When the tension provision is canceled, switching of theauxiliary thread tensioner between action and inaction, i.e., switchingbetween provision of tension and cancellation thereof is carried out byoperation of a manual operation member such as a dial, a lever, a pushbutton or a foot pedal which is provided on an outer side of the sewingmachine. In order to carry out this switching, it is possible to employa method of separating one of a pair of tension discs, which areelastically brought into contact with each other by a spring, by atension releasing pin against action of the spring, a method of pushinga portion of the peripheral edge of one of the pair of tension discswith a pawl for inclining the tension disc and expanding the one whichis opposed thereto through a thread tension shaft, or a method ofapplying a spring pressure to the tension discs or canceling thisapplication by pushing the spring or canceling the pushing of thespring, similarly to the conventional thread tensioner, for example.

According to the inventive overlock sewing machine, the thread path maybe changed or the auxiliary thread tensioner may be switched betweenaction and inaction in switching between the over-edge chain stitch andthe rolled seam, and it is not necessary to carry out tension adjustmentin switching of the stitch as to both thread tensioners.

When the thread path is changed, the mechanism of the auxiliary threadtensioner can be simplified since it is not necessary to provide amechanism for bringing the auxiliary thread tensioner into an inactionstate. When the auxiliary thread tensioner can be switched betweenaction and inaction, it is preferable to make the feed rate adjustablein association with this switching operation, i.e., a switchingmechanism for the auxiliary thread tensioner and a feed rate adjustingmechanism are preferably interlocked with each other so that the feedrate is increased when the auxiliary thread tensioner is brought into aninaction state to carry out an over-edge chain stitch while the feedrate is reduced when a rolled seam is formed through action of theauxiliary thread tensioner. To this end, an end cam for switching theauxiliary thread tensioner may be provided on a shaft of a dial for feedrate adjustment to drive the aforementioned tension releasing pin orpawl or to push the spring or cancel the pushing by the cam.

When the switching mechanism for the auxiliary thread tensioner and thefeed rate adjusting mechanism are interlocked with each other, it ispreferable that the feed rate can be adjusted in the over-edge chainstitch and the rolled seam respectively. To this end, the aforementionedend cam for switching which is provided on the shaft of the dial may beformed by a double-lift cam having high and low two types of lifts sothat the shaft of the dial can be rotated by constant amountsrespectively while not changing the state of tension provision orcancellation and the feed rate adjustment is carried out in therespective rotation ranges.

In another overlock sewing machine according to the present invention,therefore, a switching mechanism for switching the auxiliary threadtensioner to action or inaction is provided. Thus, the thread path maynot be changed in switching between an over-edge chain stitch and arolled seam. When the switching mechanism and the feed rate adjustingmechanism are formed to be interlocked with each other, switching of theauxiliary thread tensioner to action or inaction and adjustment of thefeed rate can be carried out by operation of one manual operationmember. In the other overlock sewing machine according to the presentinvention, further, adjustment of the feed rate can be carried out inswitching between the over-edge chain stitch and the rolled seamrespectively in an overlock sewing machine interlocking the switchingmechanism for the auxiliary thread tensioner and the feed rate adjustingmechanism with each other. Thus, the feed rate can be adjusted also inthe rolled seam in addition to the over-edge chain stitch.

In the other overlock sewing machine according to the present invention,further, the cam for switching the auxiliary thread tensioner to actionor inaction is formed as a double-lift end cam having high and low twotypes of lifts, and mounted on the shaft of the dial of the feed rateadjusting mechanism. Thus, the end cam can be rotationally operatedthrough the feed rate adjusting mechanism.

In the other overlock sewing machine according to the present invention,further, the main thread tensioner and the auxiliary thread tensionerare so arranged that the thread paths of the respective threadtensioners are positioned in the same plane so that threads can bereadily passed through the thread tensioners. Thus, thread passage canbe carried out by unidirectionally operating the threads on theaforementioned same plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a conventional ordinary over-edgechain stitch with one needle and three threads.

FIG. 2 is a perspective view showing a conventional rolled seam with oneneedle and three threads.

FIG. 3 is a front elevational view showing an overlock sewing machinewith one needle and three threads according to an embodiment of thepresent invention.

FIG. 4 is a side elevational view of the overlock sewing machine shownin FIG. 3.

FIG. 5 is a partially fragmented plan view of an auxiliary threadtensioner in an over-edge chain stitch in the overlock sewing machineshown in FIG. 3.

FIG. 6 is a partially fragmented plan view of the auxiliary threadtensioner upon switching to a rolled seam in the overlock sewing machineshown in FIG. 3.

FIG. 7 is a side elevational view showing a feed mechanism of theoverlock sewing machine shown in FIG. 3.

FIG. 8 is a perspective view showing another example of the switchingmechanism shown in FIG. 3.

FIG. 9 is a front elevational view of an overlock sewing machinecomprising the switching mechanism shown in FIG. 8.

FIG. 10 is a side elevational view of the overlock sewing machine shownin FIG. 9.

FIG. 11 is a front elevational view of an overlock sewing machinecomprising a switching mechanism of still another example of theswitching mechanism shown in FIG. 3.

FIG. 12 is a perspective view of the switching mechanism shown in FIG.11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, an overlock sewing machine with one needle and three threadsaccording to an embodiment of the present invention is described withreference to FIGS. 3 and 4.

As shown in FIG. 3, a thread tensioner 2 for a needle thread, a threadtensioner 3 for an upper looper thread and a thread tensioner 4 for alower looper thread are arranged on a front surface upper part of asewing machine cover 1. A needle thread 5 passed through the threadtensioner 2 by a spool which is not shown, an upper looper thread 7passed through the thread tensioner 3, and a lower looper thread 9passed through the thread tensioner 4 are structured to be passedthrough a needle 6, an upper looper 8 and a lower looper 10 throughprescribed thread paths respectively.

A dial 12 for fabric feed rate adjustment is protrudingly provided on aside surface of a sewing machine body 11. The fabric feed rate isadjusted by a rotational operation of this dial 12.

In the aforementioned overlock sewing machine with one needle and threethreads, an auxiliary thread tensioner 15, through which the lowerlooper thread 9 on the thread path is passed, is provided in thevicinity of the thread tensioner 4. Further, a switching lever 16 forswitching action or inaction of the auxiliary thread tensioner 15 isprovided adjacently to the dial 12. The auxiliary thread tensioner 15includes a mount 18, a screw shaft 19 which is fastened to the mount 18to project sideward, a pair of tension discs 20 which are slidablyengaged with the screw shaft 19, a spring seat 21 which is screwed tothe screw shaft 19, and a coil spring 22 which is freely engaged(movably fitted) with the screw shaft 19 between the spring seat 21 andthe tension discs 20 for pressing the tension discs 20, as shown inFIGS. 5 and 6. An upper pawl 23 and a lower pawl 24 are furtherintegrally attached to the mount 18. The upper pawl 23 is directed tothe peripheral edges of the tension discs 20, while the lower pawl 24 isengaged with an end cam 25 for switching which is fixed coaxially withthe switching lever 16.

In an over-edge chain stitch, the lower pawl 24 is engaged with a highlift part of the end cam 25, whereby the upper pawl 23 rams the tensiondisc peripheral edges to incline the tension discs 20 and to expand aportion between the tension discs on the front surface side of thesewing machine cover, so that no presser bar pressure is applied to thelower looper thread 9 which is passed between the tension discs (seeFIG. 5). In a rolled seam, on the other hand, the lower pawl 24 isengaged with a lower lift part of the end cam 25 to separate the upperpawl 23 from the tension discs 20, thereby applying tension to the lowerlooper thread 9 which is passed between the tension discs (see FIG. 6).

As hereinabove described, the auxiliary thread tensioner is switched bythe rotational operation of the switching lever 16 to inact in theover-edge chain stitch and to act in the rolled seam. Further, the lowerlooper thread 9 is provided with tension by the thread tensioner 4 whichis set at tension suitable for the over-edge chain stitch in inaction,while the tension provided by the thread tensioner 4 and tensionprovided by the auxiliary thread tensioner 15 are applied to the lowerlooper thread 9 in action so that tension which is suitable for therolled seam is provided.

When the operation is switched to the rolled seam, the auxiliary threadtensioner is made to act for increasing the tension which is applied tothe lower looper thread 9 as described above, while a presser foot and aneedle plate are replaced with parts for the rolled seam, and the feedrate is adjusted to small in general.

In this embodiment, adjustment of the fabric feed rate is carried out byrotationally operating the dial 12 for changing the inclination of atension box 26 by a feed rate adjusting cam 27 which is fixed to a dialshaft 13. Namely, a slider 28 which is engaged with the tension box 26is provided on one end with reference to FIG. 7, so that the slider 28reciprocates along the tension box 26 by rotational driving of aneccentric shaft 29. Thus, the amount of reciprocation of a horizontalfeed arm 31 reciprocating in the horizontal direction of the figure ischanged by inclination of the tension box 26, whereby the amount ofreciprocation of a feed dog 32, i.e., the fabric feed rate is changed.

In the aforementioned embodiment, the switching between action andinaction of the auxiliary thread tensioner 15 by the switching lever 16and the adjustment of the fabric feed rate by the rotational operationof the dial 12 are separately carried out independently of each other.Therefore, operations of both the switching lever 16 and the dial 12 arenecessary for switching between the over-edge chain stitch and therolled seam. However, as discussed below it is also possible to enablesimultaneous performance of the switching between action and inaction ofthe auxiliary thread tensioner and change of the feed rate only by theoperation of the dial 12.

FIGS. 8 to 10 show an example which is thus structured, and theaforementioned end cam 25 is mounted on a dial shaft 13 of a dial 12. Inthe embodiment shown in FIGS. 8 to 10, it is possible to adjust the feedrate at a time of carrying out an over-edge chain stitch and at a timeof forming a rolled seam respectively. Namely, a pin 36 which isprotrudingly provided on a coupling plate 35 is engaged with a camgroove 34 which is formed in a feed rate adjusting cam 27. Thus, atension shaft 38 is rotated through the coupling plate 35 and a lever 37by rotation of the feed rate adjusting cam 27, whereby inclination of atension box 27 is changed. In this case, a lower pawl 24 is engaged witha high lift part of the end cam 25 so that an over-edge chain stitch iscarried out until the pin 37 is in the range of cam groove parts a to e,and the feed rate is increased from the point a where the feed rate iszero toward a point b, a point c and a point d, so that the feed rate ismaximized at the point e. Until the pin 37 is in the range of cam grooveparts A to B, on the other hand, the lower pawl 24 is engaged with alower lift part of the end cam 25 so that a rolled seam is formed, andthe feed rate is increased from A toward B. A locating spring 40 shownin FIG. 10 is engaged with/stopped at a notch groove 41 which is formedin the peripheral surface of the feed rate adjusting cam 27, foradjustment to typical feed rates in the over-edge chain stitch and inthe rolled seam.

With reference to FIGS. 11 and 12, an example of an overlock sewingmachine comprising still another switching mechanism is now described.In this example, an end cam 25 is formed on a peripheral edge of a feedrate adjusting cam 27, and a spring cap 45 of a coil spring 24 isslidably engaged in a shaft 44 of an auxiliary thread tensioner 15. Apresser plate 47 pressing the spring cap 45 is rotatably pivotallysupported on a support block 46 which is freely engaged with a dialshaft 13 with axial movement being restricted by a retaining ring 49. Apin 48 which is engaged with the end cam 25 is protrudingly provided onone side end of the presser plate 47.

When an over-edge chain stitch is carried out in such an apparatus, thepin 48 is engaged with a lower lift part of the end cam 25 to inclinethe presser plate 47 leftward in the figure. Then, the spring cap 45 ismoved leftward by action of the coil spring 22, and the coil spring 22is brought into a sufficiently extended state. Thus, no spring pressureof the coil spring 22 acts on tension discs 20, to apply no tension to alower looper thread which is passed through the tension discs as theresult. When a feed rate adjusting cam 27 is rotated by operation of thedial 12 in such a range that the pin 48 is engaged with the lower liftpart of the end cam 25, the feed rate in the over-edge chain stitch isadjusted.

When a rolled seam is formed, on the other hand, the pin 48 is engagedwith a high lift part of the end cam 25 to incline the presser plate 47rightward in the figure. Thus, the spring cap 45 is moved rightwardagainst the action of the coil spring 22. Thus, tension is applied tothe lower looper thread which is passed through the tension discs. Inthis case, adjustment of the feed rate in the rolled seam is possible insuch a range that the pin 48 is engaged with the high lift part of theend cam 25.

INDUSTRIAL AVAILABILITY

The overlock sewing machine according to the present invention iscapable of readily forming a rolled seam with no requirement for acomplicated tension adjusting operation. Therefore, it is widelyapplicable to an overlock sewing machine forming a rolled seam inaddition to an over-edge chain stitch.

We claim:
 1. An overlock sewing machine, comprising:a main threadtensioner for providing a lower looper thread or a looper thread withthread tension being necessary for forming an ordinary over-edge stitch;and an auxiliary thread tensioner for providing said lower looper threador looper thread with thread tension being necessary for forming arolled seam along with said main thread tensioner, wherein the auxiliarythread tensioner comprises a pair of tension disks which can beadjustable inclined relative to one another, the disks being inclined toexpand a spacing defined between them such that no pressure is appliedby the disks to the lower looser thread passed therebetween.
 2. Theoverlock sewing machine in accordance with claim 1, wherein:the threadpath of said lower looper thread or looper thread is not passed throughsaid auxiliary thread tensioner in an over-edge chain stitch, and passedthrough said auxiliary thread tensioner in a rolled seam.
 3. Theoverlock sewing machine in accordance with claim 1, further including:aswitching mechanism for switching said auxiliary thread tensionerbetween action and inaction by a manual operation.
 4. The overlocksewing machine in accordance with claim 3, further comprising:a feedrate adjusting mechanism being formed to be interlocked with saidswitching mechanism.
 5. The overlock sewing machine in accordance withclaim 4, wherein:the feed rate of said feed rate adjusting mechanism isadjustable in an over-edge chain stitch and a rolled seam respectively.6. (Amended) The overlock sewing machine in accordance with claim 5,wherein:said feed rate adjusting mechanism includes:a feed rateadjusting cam having a feed rate adjusting cam part for an over-edgechain stitch and a feed rate adjusting cam part for a rolled seam. 7.The overlock sewing machine in accordance with claim 4, wherein:saidswitching mechanism includes an end cam for switching said auxiliarythread tensioner to action or inaction, said end cam being mounted on ashaft of a dial of said feed rate adjusting mechanism.
 8. The overlocksewing machine in accordance with claim 1, wherein:said main threadtensioner and said auxiliary thread tensioner are so arranged thatrespective thread paths are positioned in the same plane.